Pierce and clinch nuts were first invented by the predecessor in interest of the assignee of this application over 50 years ago as shown, for example, by U.S. Pat. Nos. 3,089,360, 3,091,843 and 3,152,628. As shown in such patents, the original pierce and clinch nuts were T-shaped in cross-section having a projecting pilot portion and integral flange portions on opposed sides of the pilot portion. Where the fastener is utilized as a pierce nut, the end face of the pilot portion is driven against a panel supported on a die member or die button and the pilot portion pierces an opening in the panel and the panel is secured to the nut by the die member as disclosed, for example, in the above-referenced U.S. Pat. No. 3,089,360. Alternatively, the fastener may be utilized as a clinch nut, wherein an opening is preformed through the panel configured to receive the pilot portion and the panel is then secured to the fastener by the die button either by deforming the projecting end of the pilot portion or by deforming the panel into grooves in the pilot portion. As used herein, the term “self-attaching female fastener,” includes both clinch and pierce nuts.
Various improvements to self-attaching female fasteners have been made by the predecessor in interest of the assignee of this application primarily to improve the push-off strength or retention of the fastener to the panel as disclosed, for example, in U.S. Pat. Nos. 3,648,747 and 4,971,499. The self-attaching female fasteners disclosed in these patents include a central pilot portion, flange portions on opposed sides of the pilot portion each having a planar bearing face as described above; however, the panel bearing faces each include a “re-entrant groove” which provide significantly improved push-off strength when installed in a metal panel. As used herein, the term “re-entrant groove” includes opposed inclined side walls and a bottom wall, wherein the inner side wall is inclined outwardly from the bottom wall toward the outer side wall and the outer side wall is inclined inwardly toward the inner side wall forming a restricted opening to the grooves, wherein the width of the grooves adjacent the panel bearing or support faces of the flange portions are less than the width of the grooves adjacent the bottom wall. As disclosed in these patents, the bottom wall is flat and parallel to the panel support faces of the flange portions.
The method of installing the self-attaching female fasteners disclosed in these patents is similar to the method of installing the T-shaped self-attaching fasteners described above. That is, a metal panel is supported on a die button having projecting clinching lips and the pilot portion is driven through an opening in the panel and the projecting lips or “clinching lips” of the die button are driven against the panel, wherein the clinching lips deform panel portions adjacent the panel opining into the grooves and against the bottom wall. Where the self-attaching nut is used as a pierce nut, the pilot portion pierces a slug from the panel, forming the opening through the panel as described above. However, in this embodiment, the end faces of the clinching nuts deform panel portions adjacent the panel opening against the bottom wall of the groove deforming the panel portions inwardly against and beneath the inclined inner side wall of the grooves and outwardly against and beneath the inclined outer side wall of the grooves forming a more secure installation having greater push-off strength.
In a typical application of a self-attaching female fastener of the types described above, the self-attaching female fasteners are fed to an installation head having a reciprocal plunger generally attached to the upper die shoe of a die press and the die button is installed in the lower die shoe of the die press. A panel is received on the die button and, upon closing of the die press, the plunger drives the fastener through a plunger passage into the panel to install the self-attaching female fastener in the panel as described above. The panel may be simultaneously formed in the die press and the die press may include multiple installation heads and die buttons to simultaneously install a plurality of self-attaching female fasteners in the panel. Various means are utilized to feed the self-attaching female fasteners to the installation head. For example, the self-attaching female fasteners may be fed to the installation head in bulk or the fasteners may be interconnected by frangible connector elements in a continuous strip of fasteners, wherein the plunger simultaneously shears a fastener located in the plunger passage from the fastener strip and installs the fastener in a panel as described in U.S. Pat. No. 3,845,860, also assigned to the predecessor in interest of the assignee of this application. In a preferred embodiment, the frangible connector elements are frangible wires, which may be formed of any suitable frangible material, which are installed in linear grooves on the back face of the fasteners on opposed sides of the fastener bore, preferably aligned with the fastener grooves as also disclosed in the above-referenced U.S. Pat. No. 4,971,499.
As will be understood by those skilled in this art, the self-attaching female fasteners described above may be formed in a rolling mill, wherein the desired cross-sectional shape of the self-attaching female fastener is rolled from a steel wire, the bores are punched or pierced through the pilot portion, the fasteners are cut to length and the bore may then be tapped or internally threaded. However, it is difficult to accurately roll the desired shape of the re-entrant groove because the fastener strip must be very accurately located relative to the forming rolls and it is presently not possible to balance the rolling forces in a conventional self-attaching nut configuration. Where the self-attaching fasteners are to be interconnected by frangible connector elements in a strip form, as described above, the wire grooves are rolled into the back face of the strip during roll forming of the fasteners and wires are then inserted into the grooves and secured.
As will also be understood by those skilled in this art, one limitation upon applications for self-attaching female fasteners of the type described is panel thickness. That is, the self-attaching female fasteners described above have a limited range of panel thicknesses which will provide a good installation. Further, although the self-attaching female fasteners having a re-entrant groove described above provide excellent push-off strength, further improvements can be made, particularly for heavy metal applications. It is also desirable to pack, but not to completely fill the re-entrant grooves with panel metal to avoid damage to the clinching lips of the die button and not cause thread closure.
Various attempts have been made by the predecessor in interest of the assignee of this application and others to improve the integrity of the joint formed between the fastener and the panel by modifying the shape of the grooves which receive the panel during installation of the fastener, beginning with U.S. Pat. Nos. 3,299,500 and 3,724,520, both assigned to the assignee of the predecessor in interest of the assignee of this application U.S. Pat. Nos. 3,213,914, 3,253,631 and 4,119,827 also disclose various embodiments of self-attaching fasteners having grooves configured to provide improved retention or prevent rotation of the fastener relative to the panel following installation. The above-referenced U.S. Pat. Nos. 3,299,500 and 2,944,642 do disclose panel receiving grooves having a generally V-shaped bottom wall; however, the grooves are not re-entrant grooves and the method of installing a self-attaching fastener disclosed in U.S. Pat. No. 3,299,500 requires deformation of the pilot portion during installation to achieve sufficient push-off strength.
There is, therefore, a continuing need for improvements in self-attaching female fasteners which are easier to form and which provide improved push-off strength, particularly in thick or heavy metal panel applications. These objects are achieved with the self-attaching female fastener and method of installation of this invention.